1. Field of the Invention
The present invention relates to pulverized coal burners, and more particularly, to systems for delivering pulverized coal to coal fired burners.
2. Description of Related Art
A variety of devices and methods are known in the art for delivering pulverized coal to coal fired burners. Of such devices, many are directed to improving particle distribution within coal piping systems for delivering coal to be combusted.
Coal powered plants require an efficient means of supplying coal as fuel to produce heat power. Raw coal is typically pulverized in a coal pulverizer or mill to produce small coal particles or coal dust. The pulverized coal must then be delivered to a furnace or burner where it can be used for combustion. This is typically done with a coal piping system that utilizes air flows to transport pulverized coal particles from the mill or pulverizer to a nozzle where coal particles are injected into the coal burner or furnace. As the coal particles travel in the air flow through the piping system, bends in the piping and the pipe geometry in general tend to cause non-uniform coal particle distribution. A densely packed region of coal particles extending through a piping system is referred to a coal “rope.”
Coal roping causes various technical problems for operation and maintenance of coal systems. The poor distribution of coal particles can extend into the combustion zone, where localized imbalances in the fuel/air mixture tend to cause inefficient combustion and elevated emissions of NOX, CO, and other pollutants. It can also cause elevated levels of unburned carbon in the fly ash, which will lower combustion efficiency. Also, the highly abrasive nature of the coal rope impacting and scrubbing components of the coal piping and burning system causes extensive erosion of pipes and other components in the system, leading to frequent need for inspection, repairs, and replacement of parts. If inspections, repairs and replacements are not performed in a timely manner, there is an elevated chance that abrasion from coal roping will cause expensive or dangerous failures of key components.
Various solutions to the coal roping problem are known in the art. One exemplary system is described in U.S. Pat. No. 6,840,183 to Wark, which describes a diffuser for pulverized coal delivery pipes for use between a piping elbow and a burner nozzle. The diffuser includes several diffuser bars running in line with the surrounding pipe, several radial collision-style diffuser rings attached at different points along the length of the diffuser bars, and a venturi ring upstream of the other components. The diffuser is configured to be installed downstream of an elbow in the pipes by opening the elbow, inserting the diffuser, and attaching the diffuser within the piping. When in place, the diffuser can improve particle distribution downstream of the elbow. The installation requires a pipe elbow that can be opened wide enough to admit the diffuser. The considerable length of the diffuser requires an accommodating length of straight pipe between the elbow and the burner nozzle. Moreover, the length of the diffuser, the multiple collision-style deflector rings and diffuser bars lead to inevitable pressure loss for the piping system. In a typical system, the diffuser described by Wark can impart a pressure loss of 3 inH2O or more.
Such conventional methods and systems generally have been considered satisfactory for their intended purpose. However, there still remains a continued need in the art for methods and devices that are easy to install and that can be used in a variety of systems. There also remains a need in the art for such methods and devices that impart low pressure drop, while improving coal particle distribution. The present invention provides a solution for these problems.